Gear pump or motor

ABSTRACT

In a gear pump or motor, the tooth profile of the intermeshing gears is involutely formed at least on a torque transmitting side. The tooth profile of the intermeshing gears on a non-torque transmitting side is made steeper than an imaginary tooth profile which is symmetrical with that on the torque transmitting side.

United States Patent Kita et al. June 18, 1974 4] GEAR PUMP OR MOTOR2,752,751 7/1956 Vaucher 74/462 X [75] 5''" bmh FOREIGN PATENTS 0RAPPLICATIONS 22,001 10/1907 G 'tB 't 74/462 731 Assignee: ShimadzuSeisakusho Ltd., Kyoto, m n m Japan G Primary Examiner-Leonard H. erin[22] 1972 Attorney, Agent, or Firm-Morgan, Finnegan, Durham [21] Appl.No.: 283,823 & Pine [30] Foreign Application Priority Data Aug. 28, 1971Japan 46-66123 [57] ABS CT In a gear pump or motor, the tooth profile ofthe inter- 52] us. Cl. 74/462 meshing gears is involutely fomed at leaston a torque [51] Illt. Cl. F1611 transmitting side The tooth profile ofthe intermesh [58] Fleld of Search 74/462, 460 g gears on a non torquetransmitting Side is made steeper than an imaginary tooth profile whichis sym- [56] uNlTE g gg z gs g rENTs metrical with that on the torquetransmitting side.

462,073 10/1891 Beauregard 74/462 8 Claims, 6 Drawing FiguresPATENTEDJUM 1 a 1914 SHEET 2 [1F 2 GEAR PUMP R MOTOR BACKGROUND OF THEINVENTION This invention generally relates to gear pumps or motors. Inparticular this invention relates to an improvement of the intermeshinggears of the gear pump or motor.

It is a common practice to use involute teeth for the intermeshing gearsof the gear pump or motor for such reasons as easy workability, higherfinishing accuracy, etc. However, a conventional gear pump or motorhaving involute tooth gears incorporated therein cannot escape afluctuation in the fluid discharge which in turn leads to undesired aswell as uncomfortable noise production during operation. Explained indetail, the amount of fluid discharged from the gear pump or motorchanges from moment to moment and it reaches a maximum level at theinstant when the gears intermesh with each other at the pitch point.While on the other hand, the amount of the discharged fluid at theinstant when the gears intermesh with each other at points other thanthe pitch point is smaller than the maximum level. In other words, thefluid discharge of the gear pump or motor fluctuates from moment tomoment and this fluctuation of the fluid discharge is a major, thoughnot a sole, cause for the undesired noise production in the gear pump ormotor during operation. This is particularly true when the gear pump ormotor is operated at higher pressures.

It should be noted at this time that the undesired operating noise ofthe gear pump or motor is diminished to a great extent by reducing thefluctuation of the fluid discharge rate to a minimum level. In one wayor other, the fluctuation in the fluid discharge, in turn, iseffectively reduced by increasing the number of the gear teeth of theintermeshing gears. However, as can be readily understood by thoseskilled in the art, when the number of the gear teeth of a gear isincreased with the pitch circle being the same, the height of the geartooth is diminished in inverse proportion. On the other hand,

the amount of fluid discharged from the gear pump during one rotation ofthe gear (hereinafter referred to as displacement volume) changes indirect proportion to the tooth height of the gear. The result is thatthe displacement volume of the gear pump is substantially reduced if thenumber of the gear teeth of the intermeshing gears is increased with thepitch circles of the gears being the same. Thus, it is undesirablynecessary to have a large-sized gear pump to obtain a particulardisplacement volume.

Meanwhile, public restrictions on the noise of hydraulic pumps andmotors and other rotating machines are being tightened in recent years.Also there is an increasing demand for compact, low cost as well ashighly efficient hydraulic pumps in the industry.

Accordingly, it is the principal object of this invention to provide anew and improved gear pump or motor having intermeshing gears of aninvolute tooth profile which enables to provide a geater number of thegear teeth on a gear sufficient to attenuate the operating noise of thegear pump or motor without causing the above mentioned undesirablereduction in the effective tooth height of the gears.

SUMMARY OF THE INVENTION According to this invention, a gear pump ormotor includes a casing and at least one pair of intermeshing gearslocated within the casing as in any conventional gear pumps or motors.The tooth profile of the intermeshing gears according to this inventionis involutely formed at least on the torque transmitting side, while onthe opposite side, namely, the non-torque transmitting side it is notnecessarily formed involutely. However, the tooth profile on thenon-torque transmitting side is made at least steeper than an imaginaryprofile which is symmetrical with the profile on the torque transmittingside. By this arrangement of the tooth profile, it becomes possible toreduce tooth thickness without changing the tooth height, thereby makingit possible to provide a greater number of the gear teeth on the gear.In other words, the tooth profile according to this invention is a kindof tall involute tooth profile which enables to form a gear of asmallest possible circular pitch without changing the tooth height.

In a preferred embodiment of this invention, for reasons of manufactureand assembly the tooth profile on the non-torque transmitting side mayalso be formed involutely. In such case, the pressure angle on thetorque transmitting side is selected at a greater value than thepressure angle on the non-torque transmitting side, thus resulting in anon-symmetrical tooth form. For example, intermeshing gears of anon-symmetrical tooth profile having a pressure angle of 23 on thetorque transmitting tooth surface and a pressure angle of on thenon-torque transmitting tooth surface may be suitably used in accordancewith this invention.

The invention itself together with advantages thereof may be betterunderstood by referring to the following more detailed description takenin conjunction with the drawing,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of agear pump having incorporated therein intermeshing gears embodying thisinvention;

FIG. 2 is a schematic illustration of a prior-art standard basic rack;

FIG. 3 is a schematic illustration similar to FIG. 2 of another basicrack having an increased number of the gear teeth with the same pitchdiameter and tooth height as in the basic rack of FIG. 2 and with areduced circular pitch;

FIG. 4 is a schematic illustration similar to FIG. 2 of still anotherbasic rack with a pressure angle on the torque transmitting side beingmade greater than a pressure angle on the non-torque transmitting sidein accordance with this invention;

FIG. 5 is an elevational view of a pair of gears according to thisinvention arranged in a meshed relationship with each other to form agear pump or motor; and

FIG. 6 is a fragmental view showing on an enlarged scale only one geartooth profile of one of the intermeshing gears illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andin particular to FIG. 1, the invention is illustrated in connection witha gear pump, but it will be understood that the invention may beutilized in connection with a gear motor.

The pump includes a pair of intermeshing gears 11 and 12 mounted withina cylindrical casing 13. The casing 13 comprises a cylindrical side wallbody 14 and end closures 15, 16 at opposite ends of the body 14. One endclosure 15 is hereinafter referred to as the front head while the otherend closure 16 is referred as the end cover plate. The cylindrical body14 is clamped between the front head 15 and the end cover plate 16 byfour bolts (only one of which is shown as 17) which extend through thecylindrical body 14 from the cover plate 16 to the front head 15. Theend of the bolt 17 may terminate at the front head 15 and bescrewthreaded thereinto.

The front head 15 is recessed to contain a roller bearing (not shown)and a suitable oil-seal assembly 18. A drive shaft 21 extends throughthe oil-seal assembly 18 and into the inside chamber of the casing 13 toengage and drive the drive gear 11. The gear 11 is keyed in aconventional manner to the shaft 21. The drive shaft 21 is supported onthe opposite sides of the gear 11 by a pair of bearing means 26 and 27which are in turn received within the inside of the side wall body 14. Adriven shaft is supported on the opposite sides of the driven gear 12 bya pair of bearing means 31) and 31 which are in turn received within theinside of side wall body 14.

The intermeshed gears 11 and 12 are also supported between said pairs ofbearing means 26 and 27, and between and 31, respectively. The bearingmeans 26 and 30 are at their inner ends in sliding contact and insealing relationship with the left end face of the intermeshing gears 11and 12 and abut at their outer ends the end wall 36 of the front head15. The bearing means 27 and 31 are at their inner ends in slidingcontact and in sealing relationship with the right end face of the gears11 and 12 and abut at their outer ends. The end eall 37 of the end coverplate 26. The reference numerals 40 and 41 indicates sealing means whichare inserted between the end wall 36 of the front head 11 and bearingmeans 26, 30 and between the end wall of the cover plate 16 and bearingmeans 27, 31, 38, respectively.

, Inlet and outlet ports for the fluid under pressure (not shown) areprovided in the casing 13, preferably in the front head 15 and they arecommunicated with a suction side and a discharge side of the meshedgears, respectively, via fluid passageways in a conventional manner. Thefluid passageways may be arranged in any suitable manner. However, it ispreferable to arrange those passageways such that the fluid underpressure may be introduced into the suction side of the meshed gears 11,12 and released from the discharge side thereof in an axial direction ofthe gears. Also, in order to avoid fluid entrapping when the two gearsengage with each other at two points simultaneously, escape channels forthe entrapped fluid may be suitably formed in bearing means 26, 27, 30and 31.

Either spur or helical gears are used for the intermeshing gears. Inaccordance with this invention, the tooth profile at least on the torquetransmitting side is involutely formed. In a preferred embodiment ofthis invention the tooth profile is formed involutely on both the torquetransmitting and non-torque transmitting sides. In the latter case, theinvolute tooth profile is designed such that the pressure angle on thetorque transmitting side is greater than the pressure angle on thenon-torque transmitting side. By this unique design of the toothprofile, a tall involute tooth gear with a smallest possible pitchcircle is obtained without reducing the original tooth height. Whenemployed in a gear pump or motor, the tall involute tooth gear of thisinvention is effective to substantially reduce the fluctuation of thefluid discharge from the gear pump thereby attenuating the operatingnoise of the gear pump to a minimum level. For ease of understanding,the unique tall involute gear of this invention together with its noisereducing effect will be explained in more detail having reference to thebasic racks which are schematically illustrated in FIGS. 2 to 4.

Generally, in the involute tooth profile of a standard tooth height,when the circular pitch is represented by 1rm the addendum and dedendumare respectively equal to m. FIG. 2 shows such a conventional standardbasic rack. in order to increase the number of the gear teeth K times asmany (where K 0) with the pitch diameter and the tooth height of thestandard basic rack of FIG. 2 unchanged, the circular pitch thereof isdecreased to UK. This basic rack is schematically illustrated in FIG. 3.

In the case of the basic racks shown in FIGS. 2 and 3 where the pressureangles on the opposite tooth surfaces of the profile are equal to eachother, the available increase in the number of the gear teeth isdetermined as well as limited by the presence of a minimum allowableland thickness at the tooth top. If K is increased over this upperpermissible limit without changing the originally selected pressureangles, the addendum is substantially reduced. If it is attempted todecrease the pressure angles on the other hand, the resulting undercutreduces the effective length of the involute curve at the dedendum. Whenthe effective length of the involute curve at the dedendum is shortenedbeyond a predetermined critical point, the contact interval of theintermeshing gears become less than unity, failing to assure continuousmeshing operation. For the two general reasons described above, there islittle room for selecting values greater than unity for Kin the advancedtooth profiles of recent development.

The present invention has devised a unique tooth profile as shown inFIG. 4 on the basis of the fact that the higher pressure side in gearpumps is invariably predetermined in almost all applications and hencethe tooth surface of the gear for transmitting driving force by meshingengagement with other mating gear is also predetermined (the toothsurface on the opposite side is just spaced away from the correspondingtooth surface of the mating gear by an amount equal to a backlash) andthat the fluid discharge from a gear pump (including the instantaneousfluid discharge thereof) depends substantially on the profile of thetooth surface which transmits force by the meshing engagement.

In the basic rack illustrated in FIG. 4 the pressure angle 011 on thetorque transmitting side of the gear tooth is maintained large enough tohave a contact interval of not less than unity, while the pressure angle(12 on the non-torque transmitting side is made relatively smaller thanthe pressure angle al but large enough to secure a proper tooth top landfor avoiding an excessive sharp tooth top which is harmful tosatisfactory intermeshing operation of the gears. It should be noted atthis point that even if the contact interval on the non torquetransmitting side of the gear tooth is reduced to less than unity due tothe presence of the larger undercut, it causes no harmful effect on thedesired intermeshing operation of the gears.

Following is a more specific example of the preferred design of the gearaccording to this invention:

Pressure angle (11 on the torque transmitting side l4.5 Assuming thenumber of the gear teeth to be 12,

then; Tooth height module/pitch module z 1.3 This means that thedisplacement volume is increased by 30 percent. If it is attempted toobtain the same tooth height as in the gear of the present inventionusing the conventional standard tooth profile with the same pitchdiameter, the number of the gear teeth is as follows;

Meanwhile, the percentage fluctuation or pulsation of the instantaneousfluid discharge of the gear pump using a pair of intermeshing gearshaving nine teeth, respectively, is approximately 24 percent, whereas itis approximately 18 percent when intermeshing gears each having twelveteeth is employed. Thus, by using the tooth profile of this invention,the fluctuation of the fluid discharge is effectively reduced tothree-fourths of that when the conventional tooth profile is used. Thisresults in a substantial reduction of noise which is produced duringoperation of the gear pump or motor.

The unique tooth profile has been explained hereinabove having referenceto the basic racks. In actual practice, a pair of gears having gearteeth of the aboveexplained profile are arranged in an intermeshing relationship within a gear pump or motor casing as illustrated in FIG. 5.FIG. 6 shows in an enlarged scale the profile of only one gear tooth inone of the meshed gears of FIG. 5. In FIG. 5, a drive gear 11 isarranged in an intermeshing relationship with a driven gear 12 and isadapted to rotate in clockwise direction thereby to drive the drivengear in counter-clockwise direction. In the meshed section of the gears,the left hand tooth surface of each of the gear teeth in the drive gear11 as seen in FIG. 5 is the torque transmitting tooth surface, while theright hand tooth surfaces of the same gear are the non-torquetransmitting surfaces. The reverse is true with the driven gear 12.Thus, the torque transmitting tooth surfaces of the gears 11 and 12 areindicated at 41, while the non-torque transmitting tooth surfaces areindicated at 42. As is apparent from the drawing, the pressure angle onthe torque transmitting tooth surfaces 41 is made greater than thepressure angle on the other non-torque transmitting tooth surfaces 42.As the result, the tooth profile on the non-torque transmitting side isinclined steeper than an imaginary profile which is symmetrical withrespect to that on the torque transmitting side.

In FIG. 6, the torque transmitting tooth surface 41 is involutely formedat the pressure angle of 23. On the non-torque transmitting side, thetooth surface 42 is involutely formed at the pressure angle of l4.5along the addendum portion 42a. The dedendum portion 42b of thenon-torque transmitting surface 42 is cut away to avoid undercuttinginterference with the gear teeth of the mating gear.

In the illustrated embodiment, the greater pressure angle on the torquetransmitting side is selected at 23,

while the smaller pressure angle on the non-torque transmitting side atl4.5. However, different pressure angles may be suitably employed. Inactual practice, the pressure angle on the torque transmitting side maybe within the range of 14 to 30. Concerning the pressure angle on thenon-torque transmitting side, there is no significance to define thepressure angle on this side since the non-torque transmitting toothsurface does not participate in the intermeshing engagement. However, itmay be suitably determined depending on such factors, for example, as anamount of undercut, a minimum allowable tooth top land and tooththickness necessary to maintain the desired tooth strength. In actualpractice, it is preferred to select the pressure angle on the non-torquetransmitting side within the range of 0 and 20. Also, in the illustratedembodiment, the tooth profile on the torque transmitting side has beenformed involutely at least along its addendum. However, the toothprofile on the torque transmitting side is not necessarily be limited tothe involute tooth profile and any other suitable tooth profile may beemployed.

The important point is that the tooth profile on the non-torquetransmitting side is formed steeper than the imaginary tooth profilewhich is symmetrical with the tooth profile on the torque transmittingside in order to reduce the tooth thickness to a possible minimumthereby to provide a tall tooth type intermeshing gear with a greatestpossible number of gear teeth. Thus, any suitable form may be chosen asthe tooth profile on the non-torque transmitting side includingstraight-line and cliff-like profiles.

It will be understood that the construction hereinabove described can beused not only as a gear pump but also as a gear motor.

As is apparent from the foregoing explanation, in the involute toothprofile for the intermeshing gears to be used in a gear pump or motoraccording to this invention the pressure angle on the torquetransmitting side is made relatively greater than the pressure angle onthe non-torque transmitting side. A gear pump which incorporatesintermeshing gears of this invention pro duces only a substantiallyreduced noise while displacing an increased amount of fluid as comparedto a gear pump having intermeshing gears of the conventional standardtooth profile with the same pitch diameter, tooth thickness and toothheight.

While only a few preferred embodiments have been described above, it isto be understood that this invention is not limited to the particularembodiment disclosed and that it is intended to cover all modificationswhich are within the true sprit and scope of the invention as claimed.

What is claimed is:

1. In a gear pump or motor including a casing and at least one pair ofintermeshing gears arranged within said casing, an improvement in whichthe tooth profile of said intermeshing gears is formed involutely atleast on the torque transmitting side and the tooth profile on thenon-torque transmitting side is made steeper than an imaginary toothprofile which is symmetrical with that on the torque transmitting side.

2. An inprovement according to claim 1, in which the tooth profile isinvolutely formed! on both the torque transmitting and non-torquetransmitting sides and the pressure angle on the non-torque transmittingside is made smaller than the pressure angle on the torque transmittingside.

3. An improvement according to claim 2, in which the pressure angle onthe torque transmitting side is se lected within the range of 14 and 30while the pressure angle on the non-torque transmitting side is selectedwithin the range of and 20.

4. An improvement according to claim 3, in which the pressure angle onthe torque transmitting side is selected at 24 while the pressure angleon the nontorque transmitting side is selected at l4.5.

5. In a gear pump or motor including a casing and at least one pair ofintermeshing gears arranged within said casing, and wherein saidintermeshing gears each include a plurality of teeth each having a topland surface portion of a non-symmetrical profile, the improvementtherein which comprises: the non-torque transmitting side of each geartooth profile has a steeper angle of inclination with respect to saidtop land than the angle of inclination of the torque transmitting side 8of each gear tooth profile with respect to said top land.

side of the tooth profile is formed involutely.

1. In a gear pump or motor including a casing and at least one pair ofintermeshing gears arranged within said casing, an improvement in whichthe tooth profile of said intermeshing gears is formed involutely atleast on the torque transmitting side and the tooth profile on thenon-torque transmitting side is made steeper than an imaginary toothprofile which is symmetrical with that on the torque transmitting side.2. An inprovement according to claim 1, in which the tooth profile isinvolutely formed on both the torque transmitting and non-torquetransmitting sides and the pressure angle on the non-torque transmittingside is made smaller than the pressure angle on the torque transmittingside.
 3. An improvement according to claim 2, in which the pressureangle on the torque transmitting side is selected within the range of14* and 30* while the pressure angle on the non-torque transmitting sideis selected within the range of 0* and 20*.
 4. An improvement accordingto claim 3, in which the pressure angle on the torque transmitting sideis selected at 24* while the pressure angle on the non-torquetransmitting side is selected at 14.5*.
 5. In a gear pump or motorincluding a casing and at least one pair of intermeshing gears arrangedwithin said casing, and wherein said intermeshing gears each include aplurality of teeth each having a top land surface portion of anon-symmetrical profile, the improvement therein which comprises: thenon-torque transmitting side of each gear tooth profile has a steeperangle of inclination with respect to said top land than the angle ofinclination of the torque transmitting side of each gear tooth profilewith respect to said top land.
 6. The improvement as claimed in claim 5,wherein the profile of the torque transmitting side of each of said gearteeth is formed involutely at least along the addendum portion thereof.7. The improvement as claimed in claim 6, wherein the dedendum portionof the profile of the non-torque transmitting side of each of said teethis undercut with respect to the addendum portion thereof.
 8. Theimprovement as claimed in claim 7, wherein the addendum portion of thenon-torque transmitting side of the tooth profile is formed involutely.